U.S. patent number 4,085,358 [Application Number 05/641,786] was granted by the patent office on 1978-04-18 for regulated dc to dc power supply with automatic recharging capability.
This patent grant is currently assigned to Texas Instruments Incorporated. Invention is credited to Stanley W. Holcomb.
United States Patent |
4,085,358 |
Holcomb |
April 18, 1978 |
Regulated DC to DC power supply with automatic recharging
capability
Abstract
A DC to DC power supply, which includes simplified semiconductor
circuitry and has features enabling the semiconductors to become
non-conducting when the output is unloaded or causing battery
connected to the input to charge when a higher than normal output
voltage is applied to the circuit output.
Inventors: |
Holcomb; Stanley W.
(Richardson, TX) |
Assignee: |
Texas Instruments Incorporated
(Dallas, TX)
|
Family
ID: |
24573842 |
Appl.
No.: |
05/641,786 |
Filed: |
December 29, 1975 |
Current U.S.
Class: |
320/127; 320/140;
363/16 |
Current CPC
Class: |
H02M
3/156 (20130101) |
Current International
Class: |
H02M
3/156 (20060101); H02M 3/04 (20060101); H02J
007/00 () |
Field of
Search: |
;323/DIG.1,17
;321/2,45ER ;320/21,2,3,5,9,14,DIG.1,23,39 ;307/11,151,66
;363/16-26 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
2,234,121 |
|
Feb 1973 |
|
DT |
|
2,353,345 |
|
May 1974 |
|
DT |
|
1,273,019 |
|
May 1972 |
|
UK |
|
Primary Examiner: Beha, Jr.; William H.
Attorney, Agent or Firm: Comfort; James T. Grossman; Rene'
E. Berg; Richard P.
Claims
What is claimed is:
1. An electrical circuit comprising: an input, an output, voltage
responsive means connected to said input and normally responsive to
the application of a first electrical potential thereto to change
successively between first and second electrical conditions thereby
to develop a second electrical potential at said output, said
second electrical potential being a higher potential than said
first electrical potential and control means, interconnecting said
voltage responsive means and said output, for interrupting said
successive change when the potential at said output rises to a
first predetermined level and for conducting current from said
output to said input when the potential at said output is at a
second predetermined level higher than said first predetermined
level.
2. The circuit according to claim 1, further including a battery
coupled to said input.
3. The circuit according to claim 2, wherein said battery is a
rechargeable battery.
4. The circuit according to claim 1, wherein said first
predetermined level is a DC potential.
5. An electronic circuit comprising:
an input and an output, electrical energy storage means
interconnected with said output, voltage responsive means connected
to said input and normally responsive to the application of a
predetermined potential thereto to change successively between
first and second electrical conditions thereby to develop an
electrical potential across said energy storage means, and control
means interconnecting said voltage responsive means, said storage
means and said output, effective when the potential at said output
rises to a predetermined level to interrupt said successive change
and, when the potential at said output is at a level higher than
said predetermined level to conduct current therethrough to said
input.
6. The circuit according to claim 5, furthering including a battery
coupled to said input.
7. The circuit according to claim 6, wherein said battery is a
rechargeable battery.
8. The circuit according to claim 5, wherein said predetermined
level is greater than said predetermined potential.
9. In combination with a DC to DC power supply wherein a battery is
usually connected to the circuit input and wherein a DC output
voltage, higher than battery voltage, is derived at a circuit
output, the improvement which comprises:
(a) detecting means for detecting when a predetermined voltage
higher than the normal output voltage is applied to the circuit
output, and
(b) conducting means for conducting such a detected higher voltage
to the input of the circuit whereby a rechargeable battery
connected to the circuit input will be caused to charge.
10. The apparatus as defined in claim 9, wherein said conducting
means comprises a semiconductor conducting means.
11. The apparatus as defined in claim 10, wherein said
semiconductor conducting means comprises a transistor whose emitter
is connected by circuit means to said circuit input, whose
collector is connected by collector circuit means to said circuit
output and whose base is connected by base circuit means to said
detecting means.
12. The apparatus as defined in claim 11, wherein said collector
circuit means comprises at least one resistor.
13. The apparatus as defined in claim 9, wherein said detecting
means comprises a Zener diode connected between said circuit output
and said conducting means.
14. The apparatus as defined in claim 11, wherein said detecting
means comprises a Zener diode connected between said circuit output
and said base circuit means.
15. The apparatus as defined in claim 14, wherein said base circuit
means comprises at least one resistor and wherein said collector
circuit means comprises at least one resistor.
16. A DC to DC power supply circuit comprising:
(a) a resistive device;
(b) a first semiconductor means for controlling the current flowing
through said resistive device;
(c) a single-winding inductor;
(d) a second semiconductor means for controlling the current
flowing through said single-winding inductor;
(e) circuit means coupling the control element of said second
semiconductor means with said resistive device;
(f) a feedback loop comprising at least one feedback capacitor
coupling the control element of said first semiconductor means with
said inductor;
(g) converter means connected to said inductor for converting the
energy stored in said inductor during the operation of said first
and second semiconductor means into direct current available at the
circuit output;
(h) output voltage regulator means connected to said circuit output
and to the control element of said first semiconductor means for
regulating the level of the direct current voltage developed at
said circuit output;
(i) first circuit means connecting said first semiconductor means
and its resistive device in parallel with said second semiconductor
means and its inductor to a direct current source applied at the
circuit input;
(j) second circuit means connecting one element of said input and
one element of said output to a circuit common; and
(k) third circuit means for coupling a voltage applied at said
circuit output to said circuit input when the voltage applied is
greater than the level of direct current voltage normally developed
at said circuit output.
17. A DC to DC power supply circuit as defined in claim 16, wherein
said third circuit means is a semiconductor means of the same
conductivity type as said second semiconductor means, wherein the
control element of said third semiconductor means is connected by
circuit means to said output voltage regulator means and wherein
the current carrying elements of said third semiconductor means are
resistively connected between said circuit output and said circuit
input.
18. A DC to DC power supply circuit as defined in claim 16, wherein
said first semiconductor means is of complementary conductivity
type to said second semiconductor means.
19. A DC to DC power supply circuit as defined in claim 18, wherein
said first semiconductor means is a PNP transistor and said second
semiconductor means is an NPN transistor.
20. A DC to DC power supply circuit as defined in claim 18, wherein
said first semiconductor means is an NPN transistor and said second
semiconductor means is a PNP transistor.
21. A DC to DC power supply circuit as defined in claim 17, wherein
said first semiconductor means is a PNP transistor and said second
and third semiconductor means are NPN transistors.
22. A DC to DC power supply circuit as defined in claim 17, wherein
said first semiconductor means is an NPN transistor and said second
and third semiconductor means are PNP transistors.
23. A DC to DC power supply circuit as defined in claim 18, wherein
said positive feedback loop consists of a resistor and a capacitor
connected in series and with the capacitor connected to the control
element of said first semiconductor means.
24. A DC to DC power supply circuit as defined in claim 23, wherein
unidirectional conductive means is connected in parallel with said
capacitor to improve the switching time of the circuit.
25. A DC to DC power supply circuit as defined in claim 18, wherein
unidirectional conductive means is connected to the control element
of said first semiconductor means and to the circuit input to limit
the extent to which the semiconductor junction of said control
element becomes reverse biased during circuit operation.
26. A DC to DC power supply circuit as defined in claim 25, wherein
said unidirectional conductive means is at least one semiconductor
diode.
27. A DC to DC power supply circuit as defined in claim 18, wherein
said output voltage regulator circuit means comprises at least one
Zener diode.
28. A DC to DC power supply circuit as defined in claim 18, wherein
said output voltage regulator means comprises at least one Zener
diode and at least one unidirectional conductive means connected in
series.
29. A DC to DC power supply circuit as defined in claim 18, wherein
said converter means comprises a unidirectional conductive means
and a capacitor connected in series between said inductor and said
circuit common thereby producing the output voltage of the circuit
between the junction of said capacitor and said unidirectional
conductive means and said circuit common.
30. A DC to DC power supply circuit as defined in claim 17, wherein
said output voltage regulator means comprises at least one Zener
diode and at least one unidirectional conductive means connected in
series and wherein the control element of said third semiconductor
means is resistively coupled to the junction between said Zener
diode and said unidirectional conductive means.
31. A DC to DC power supply circuit as defined in claim 18, wherein
said circuit means coupling the control element of said second
semiconductor means with said resistive load comprises at least one
resistor.
32. A DC to DC power supply circuit as defined in claim 16, wherein
said first semiconductor means is of the same conductivity type as
said second semiconductor means.
33. A DC to DC power supply circuit as defined in claim 32, wherein
said first semiconductor means and said second semiconductor means
are each a PNP transistor.
34. A DC to DC power supply circuit as defined in claim 32, wherein
said first semiconductor means and said second semiconductor means
are each an NPN transistor.
35. A DC to DC power supply circuit as defined in claim 17, wherein
said first semiconductor means, said second semiconductor means and
said third semiconductor means are each a PNP transistor.
36. A DC to DC power supply circuit as defined in claim 17, wherein
said first semiconductor means, said second semiconductor means and
said third semiconductor means are each an NPN transistor.
37. A DC to DC power supply circuit as defined in claim 32, wherein
unidirectional conductive means is connected in parallel with said
feedback capacitor to improve the switching time of the
circuit.
38. A DC to DC power supply circuit as defined in claim 32, wherein
unidirectional conductive means is connected to the control element
of said first semiconductor means and to the circuit input to limit
the extent to which the semiconductor junction of said control
element becomes reverse biased during circuit operation.
39. A DC to DC power supply circuit as defined in claim 32, wherein
said output voltage regulator circuit means comprises at least one
Zener diode.
40. A DC to DC power supply circuit as defined in claim 32, wherein
said output voltage regulator means comprises at least one Zener
diode and at least one resistor connected in series.
41. A DC to DC power supply circuit as defined in claim 32, wherein
said output voltage regulator means comprises at least one Zener
diode, at least one resistor and at least one unidirectional means
connected in series.
42. A DC to DC power supply circuit as defined in claim 32, wherein
said converter means comprises a unidirectional conductive means
and a capacitor connected in series between said inductor and said
circuit thereby producing the output voltage of the circuit between
the junction of said capacitor and said unidirectional conductive
means and said circuit common.
43. A DC to DC power supply as defined in claim 17, wherein said
output voltage regulator means comprises at least one Zener diode
connected to said circuit output, unidirectional conductive means
connected to said Zener diode and at least one resistor connected
between said unidirectional conductive means and the said control
element of said first semiconductor means wherein the control
element of said third semiconductor means is resistively coupled to
the junction between said Zener diode and said unidirectional
conductive means.
44. The circuit according to claim 16, wherein the direct current
source is a battery coupled to said input.
45. The circuit according to claim 44, wherein said battery is a
rechargeable battery.
Description
This invention relates to semiconductor DC to DC power supplies. As
is well known to those skilled in the art, successive improvements
in DC to DC power supply circuits have resulted in the highly
compact power supply circuits which are utilized in modern
battery-operated, handheld appliances, such as the handheld
electronic calculator. These circuits are necessary because the
voltages needed to operate the logic cicuitry and display devices
of these calculators are often higher than that which can be
supplied directly by a small number of standard size batteries.
This is especially true if the appliance is to utilize rechargeable
batteries, which typically supply only 1.25 volts each while
certain display devices may require as much as 30 volts to be
operable.
DC to DC power supply circuits have been relied upon to step-up the
available battery voltages to the voltage or voltages necessary to
operate the appliance rather than significantly increasing the size
and weight of the appliance to accommodate the number of batteries
otherwise necessary. DC to DC power supply circuits typical of the
prior art are depicted in FIGS. 1, 2 and 3. Each of these circuits
display certain deficiencies or drawbacks which would make their
substitution for a larger number of batteries an undesirable choice
if it were not for the overriding savings in space and weight.
These include: (1) lack of capability for automatic recharging of a
battery connected at the input when a higher than nominal output
voltage is applied at the output, (2) high current drain on the
battery, even when unloaded, so as to require the power supply to
be switched off during nonoperation lest it rapidly discharge the
battery and (3) the use of either a large number of components or
complicated components with attendant lessened reliability and
increased cost.
It is one general object of the invention to improve DC to DC power
supply circuits.
It is another object of the invention to simplify DC to DC power
supply circuits.
It is yet another object of the invention to be able to markedly
reduce the current demands made by the circuit when desired output
voltage is attained and the circuit output is unloaded.
It is still another object of the invention to be able to
automatically regulate the level of direct current voltage
developed at the circuit output.
It is yet another object of the invention to provide for automatic
recharging of a battery connected at the circuit input when a
higher than nominal output voltage is applied at the output.
In accordance with one feature of the invention, power supply
reliability is improved and cost is decreased by utilizing a small
number of simple components.
In accordance with another feature of the invention, the current
demands made by the circuit after the desired output voltage is
attained when the output is unloaded can be markedly reduced by
biasing the circuit switching semiconductors into a non-conducting
state.
In accordance with another feature of the invention, automatic
recharging of a battery connected at the input of the circuit is
attained by biasing a semiconductor device connected between the
output and input of the circuit into conduction when a higher than
nominal output voltage is applied at the output.
In accordance with another feature of the invention, the level of
direct current output voltage can be regulated.
These and other objects and features of the invention will be
evident from the following detailed description with reference to
the drawings in which:
FIGS. 1, 2 and 3 illustrate typically the prior art.
FIG. 4 is a circuit schematic depicting a first embodiment of the
invention.
FIG. 5 is a circuit schematic depicting a second embodiment of the
invention.
An embodiment of the present invention will be described in
connection with FIG. 4 wherein given a battery range between 2.0 to
3.3 volts D.C., the circuit will produce output voltages of 7.5 to
8.5 volts D.C. Although the first embodiment is thusly described,
it will be evident to one skilled in the art that other voltage
levels could be employed without departing from the principles and
spirit of the invention.
In this system, a battery 1 has a positive terminal 2 which is
connected to the emitter of transistor 4, to the emitter of
transistor 17, by way of a diode 5 to the base of transistor 4 and
by way of an inductor 13 to the collector of transistor 9. The
negative terminal 3 of the battery 1 is connected to the negative
output terminal 22, to the emitter of transistor 9, by way of
resistor 8 to the base of transistor 9 and by way of capacitor 15
to the positive output terminal 21. The collector of transistor 4
is connected by way of a resistor 7 to the base of transistor 9 and
by way of a resistor 6 to the base of transistor 4. The collector
of transistor 9 is connected by way of a diode 14 to the positive
output terminal 21 and by way of a resistor 12 to a diode 10 and a
capacitor 11 which are wired in parallel and in turn connected to
the base of transistor 4. The base of transistor 4 is connected by
way of a diode 20 and Zener diode 16 to the positive output
terminal 21. The junction between diode 20 and Zener diode 16 is
connected by way of resistor 19 to the base of transistor 17. The
collector of transistor 17 is connected by way of a resistor 18 to
the positive output terminal 21. Transistor 4 is of a complementary
conductivity type to transistors 9 and 17.
In operation, the oscillator circuit operates as follows: at the
moment the battery is initially connected to the circuit input,
transistor 4 is biased into conduction by a current flowing through
resistors 6, 7 and 8 from the base of transistor 4. Transistor 9
simultaneously is biased into conduction by the voltage drop
occurring across resistor 8 which results from the current flowing
through transistor 4. A positive feedback path through resistor 12,
capacitor 11 and diode 10 biases transistor 4 further into
conduction which in turn biases transistor 9 further into
conduction by the action of the increased voltage drop occurring
across resistor 8. This positive feedback path causes both
transistors 4 and 9 to saturate. While transistor 9 is in
saturation its collector current is increasing due to the action of
the inductor 13. The collector current will continue to increase,
storing energy in the inductor, until the current reaches a value
equal to the forward current gain of transistor 9 times the
available base current. When this value of collector current is
reached, transistor 9 will enter a nonsaturated state and the
voltage drop across the collector and emitter terminals of
transistor 9 begins to increase. This increasing voltage is fed
back to the base of transistor 4 by the feedback circuit consisting
of resistor 12 and capacitor 11, causing the base voltage to rise
temporarily. Transistor 4 is caused to enter a nonsaturated mode,
thus decreasing the transistor's collector current, which in turn
decreases the voltage drop across resistor 8. This action causes
transistor 9 to further desaturate. Diode 5 is incorporated into
the circuit to keep the voltage impressed at the base of transistor
4, when transistor 9 turns off, from exceeding the reverse bias
breakdown voltage for the base-emitter junction of transistor
4.
As both devices turn off, the voltage resulting in the inductor by
release of the energy stored therein is applied in series with the
battery, thus forward biasing diode 14 and allowing capacitor 15 to
be charged to a voltage greater than that which the battery could
supply alone. As capacitor 11 discharges, the base voltage of
transistor 4 again falls, causing transistor 4 to go into
conduction and thus repeating the hereinbefore described circuit
events in a cyclical manner.
If it were not for the operation of the output voltage regulator
circuit, which comprises diode 20 and Zener diode 16, the
oscillator circuit hereinbefore described would continue to
oscillate, storing energy in the inductor 13 when transistors 4 and
9 were turned on and transferring that energy to the capacitor 15
when the transistors turn off. The frequency at which the
oscillator operates is, of course, a function of the values of the
circuit components selected.
Now turning to the operation of the output voltage regulator
circuit, the characteristics of Zener diode 16 are so selected that
when the output voltage, that is, the voltage stored in capacitor
15, reaches the desired value, the breakdown voltage of Zener diode
16 is reached, forward biasing diode 20 and causing the voltage at
the base of transistor 4 to increase thus turning off transistor 4,
on the average, longer and to a lower current level. This action
reduces the base drive to and thus the on duration of transistor 9.
Thus the energy being stored in the inductor is reduced to equalize
the energy being transferred to and from the capacitor 15. If no
energy were being transferred from the capacitor 15, that is, if
the output were unloaded, when the desired stored output voltage
exists in capacitor 15, the circuit does not oscillate and both
transistors 4 and 9 are turned off, resulting in very little drain
on the battery. The output voltage regulator circuit does lightly
load the circuit, causing the circuit to oscillate occasionally and
briefly to maintain the desired output voltage.
When a voltage slightly greater (approximately 1/2 volt) than the
normal output voltage is applied at the output terminals 21 and 22
of the circuit, such as might be supplied by an external AC to DC
power supply commonly used to power small handheld appliances when
AC current is available, the battery charging circuit comprising
transistor 17 and resistors 18 and 19, causes the battery to
charge. When the output voltage regulator circuit causes the
oscillations to cease, the voltage at node 23 is approximately the
same as the battery voltage. When the slightly higher voltage from
an external AC to DC power supply is applied to the output
terminals, the voltage at node 23 correspondingly attains a value
slightly greater than the battery voltage, causing transistor 17 to
saturate. Transistor 17 then provides a charging path to the
battery through current limiting resistor 18.
A parallel path for recharging the battery would be available
through diodes 5 and 20 and Zener diode 16. However, if this path
were utilized, the Zener diode would have to be selected to carry
the larger currents necessary to recharge the battery. In the
preferred embodiment, such a recharging path is not utilized
because of the high cost associated with high current capability
Zener diodes having close tolerances. The current carrying
capability of the Zener diode is assured of not being exceeded so
long as the external AC to DC power supply does not apply a voltage
exceeding the normal output voltage by more than approximately 1.25
volts, because transistor 17 will go into conduction before diode 5
does as the voltage at node 23 rises above the battery voltage.
If the external AC to DC power supply might supply a voltage
exceeding the normal output voltage by more than approximately 1.25
volts, then in another embodiment additional diodes or a resistor
could be connected in series with diode 5 to assure that the
current carrying capability of the Zener diode is not exceeded.
A second embodiment of the present invention will be described in
connection with FIG. 5 wherein given a battery voltage between 3.3
to 4.5 volts D.C., the circuit will produce output voltages of 9.6
to 9.75 volts D.C. This embodiment differs from the first
embodiment in that this embodiment does not have the feature of
markedly reduced current demands when the output is unloaded, but
this embodiment exhibits superior output voltage regulation.
Although the second embodiment is thusly described, it will be
evident to one skilled in the art that other voltage levels could
be employed without departing from the principles and spirit of the
invention.
In this system, a battery 1 has a positive terminal 2 which is
connected to the emitter of transistor 4, to the emitter of
transitor 9, by way of a diode 5 to the base of transistor 4, to
the positive output terminal 20 and by way of capacitor 15 to the
negative output terminal 21. The negative terminal 3 of the battery
1 is connected to the emitter of transistor 8, by way of resistor 7
to the collector of transistor 4 and by way of inductor 13 to the
collector of transistor 9. The collector of transistor 4 is
connected to the base of transistor 9 and by way of a resistor 6 to
the base of transistor 4. The collector of transistor 9 is
connected by way of a diode 14 to the negative output terminal 21
and by way of a diode 10 and a capacitor 11 which are wired in
parallel to the base of transistor 4. The base of transistor 4 is
connected by way of a resistor 17, at least one diode 19 and Zener
diode 16 to the negative output terminal 21. The junction between a
diode 19 and Zener diode 16 is connected by way of resistor 12 to
the base of transistor 8. The collector of transistor 8 is
connected by way of a resistor 18 to the negative output terminal
21. Transistors 4, 8 and 9 are all of the same conductivity
type.
In operation, the oscillator circuit operates as follows: at the
moment the battery is initially connected to the circuit input,
transistor 9 is biased into conduction by a current flow through
resistor 7 from the base of transistor 9. Transistor 9 promptly
saturates because the collector current of transistor 9 is limited
by inductor 13 and nearly all of the battery voltage momentarily
appears across inductor 13. A feedback path through capacitor 11
and diode 10 biases transistor 4 into a nonconducting node. While
transistor 9 is in saturation its collector current is increasing
due to the action of the inductor 13. The collector current will
continue to increase, storing energy in the inductor, until the
current reaches a value equal to the forward current gain of
transistor 9 times the available base current. When this value of
collector current is reached, transistor 9 will enter a
nonsaturated state and the voltage drop across the collector and
emitter terminals of transistor 9 begins to increase. This
increasing voltage is fed back to the base of transistor 4 by the
feedback circuit consisting of diode 10 and capacitor 11, causing
the base voltage to fall temporarily. Transistor 4 is caused to
enter a conducting mode, thus increasing the collector current of
transistor 4, which in turn increases the voltage drop across
resistor 7. This action causes transistor 9 to further desaturate.
Diode 5 is incorporated into the circuit to keep the voltage
impressed at the base of transistor 4 from exceeding the reverse
bias breakdown voltage for the base-emitter junction of transistor
4.
As transistor 9 turns off, the voltage resulting in the inductor by
release of the energy stored therein is applied in series with the
battery, thus forward biasing diode 14 and allowing capacitor 15 to
be charged to a voltage greater than that which the battery could
supply alone. As capacitor 11 discharges, through resistor 6, the
base voltage of transistor 4 again rises causing transistor 4 to
turn off and thus repeating the hereinbefore described circuit
events in a cyclical manner.
If it were not for the operation of the output voltage regulator
circuit, which comprises resistor 17, diode 19 and Zener diode 16,
the oscillator circuit hereinbefore described would continue to
oscillate, storing energy in the inductor 13 when transistor 9
turns on and transferring that energy to the capacitor 15 when
transistor 9 turns off. The frequency at which the oscillator
operates is, of course, a function of the values of the circuit
components selected.
Now turning to the operation of the output voltage regulator
circuit, the characteristics of Zener diode 16 are so selected that
when the output voltage, that is, the voltage stored in capacitor
15, reaches the desired value, the breakdown voltage of Zener diode
16 is reached, forward biasing diode 17 and causing the voltage at
the base of transistor 4 to decrease, turning on transistor 4, on
the average, longer and to a higher current level. This action
reduces the base drive from and thus the on duration of transistor
9. Thus the energy being stored in the inductor is reduced to a
value to equalize the energy being transferred to and from the
capacitor 15. If no energy were being transferred from the
capacitor 15, that is, if the output were unloaded, when the
desired stored output voltage exists in capacitor 15, the circuit
does not oscillate and transistor 9 is turned off, while transistor
4 is turned on. The output voltage regulator circuit regulates the
output voltage with respect to the common positive bus, thus
changes in battery voltage are compensated for by this circuit.
When a voltage of slightly greater magnitude (approximately 1/2
volt) than the normal output voltage is applied at the output
terminals 20 and 21, such as might be supplied by an external AC to
DC power supply commonly used to power small handheld appliances
when AC current is available, the battery charging circuit
comprising transistor 8 and resistors 12 and 18, causes the battery
to charge. When the output voltage regulator circuit causes the
oscillations to cease, the voltage at node 22 is approximately zero
volts. When the slightly higher voltage from an external AC to DC
power supply is applied to the output terminals, the voltage at
node 22 correspondingly attains a value slightly negative, causing
transistor 8 to saturate. Transistor 8 then provides a charging
path to the battery through current limiting resistor 18.
Having described the invention in connection with certain specific
embodiments thereof, it is to be understood that further
modifications may now suggest themselves to those skilled in the
art, for instance: (1) Diodes and transistors of opposite polarity
from those indicated could be substituted for those indicated; (2)
Darlington pairs or other semiconductor devices could be
substituted for the transistors indicated; (3) A tapped inductor
could be utilized to obtain a plurality of output voltages; (4)
Different rectifier circuits, such as the well known voltage
doubler, could be utilized instead of the rectifier circuit
depicted; (5) A resistor could be utilized instead of diode 5. It
is intended that any and all such modifications fall within the
scope of the appended claims.
* * * * *